1. Technical Field
The present invention relates to a liquid ejecting apparatus provided with a liquid ejecting head for ejecting a liquid onto a medium such as a sheet of paper and a light reflection optical sensor for detecting an edge position of the medium, and also relates to a method for detecting a medium edge position in a liquid ejecting apparatus.
2. Background Technology
An ink jet printer has been known as one example of this kind of liquid ejecting apparatus. Provided to the printer is a carriage which moves in a movement direction (main scanning direction) intersecting with a conveyance direction for sheets of paper, and which has a liquid ejecting head (a recording head). During printing, ink droplets are ejected from the liquid ejecting head toward a sheet of paper while the carriage is being moved, whereby an image or the like is printed onto the sheet of paper (for example, Patent Documents 1-4, etc.).
In, for example, the printers described in Patent Documents 1-4, a light reflection optical sensor (an edge sensor) was provided to the carriage, and a widthwise edge position of the sheet of paper was detected by the optical sensor while the carriage was being moved in the movement direction. More specifically, a detection value from the optical sensor and a threshold value are compared against each other, and when the detection value changes to being the threshold value or lower or to being the threshold value or higher, the current sensor position is determined to be an edge detection position (edge position) of the sheet of paper.
It has been noted that an ink mist generated when the liquid ejecting head ejected the ink droplets was present in the vicinity of a movement path of the carriage, as was suspended matter such as paper dust generated from the sheet of paper due to sliding over a conveyor roller, or the like. When the suspended matter sticks and the optical sensor is sullied, there is a gradual reduction in the amount of light received thereby, whereupon this has resulted in changes to a correction amount used in order to correct for an amount of positional deviation between the edge detection position at which the edge position of the sheet of paper was detected and the actual edge position of the sheet of paper, i.e., to correct by an amount commensurate with this amount of positional deviation. In order to resolve this, in a printer apparatus described in Patent Document 1, a threshold value that is optimal for every iteration is re-determined for every iteration of printing, and thus it is possible to detect the edge position with high positional accuracy by using a threshold value that is optimal and has not been impacted even by aging changes in the surface state of a support base nor by aging changes caused by fouling of the optical sensor.
In printers described in Patent Documents 2 and 3, a rib of a support base and a portion other than the rib (a groove part) are detected by an optical sensor (a recording sheet detection sensor), a detection sensitivity of the optical sensor is determined on the basis of a comparison (ratio or difference) between respective detection voltages (output values), and a threshold value corresponding to the detection sensitivity is set. For this reason, there will be a constant amount of positional deviation between the edge detection position of when the detection value of the optical sensor crosses over the threshold value and the actual edge position, and thus the edge position can be detected at high positional accuracy when corrected with a constant correction amount corresponding to the amount of positional deviation thereof.
In Patent Document 4, the printer is provided with an optical sensor for detecting a sheet of paper and a loading part and for outputting an output signal for the respectively different output values, and with a linear encoder for detecting the position of a print head in a movement direction; the output values at a timing where the level of the detection signal of the linear encoder is switched are acquired and an approximation function indicative of the relationship between the output values and the position of the print head is calculated. A controller calculates a point of intersection where the approximation function intersects with a threshold value of the output values, and understands the position of the point of intersection to be the edge position of the paper.
Japanese Laid-open Patent Publication No. 2002-127521 (for example, paragraphs [0037]-[0052], FIG. 4, FIG. 5, etc.) (Patent Document 1), Japanese Laid-open Patent Publication No. Publication 2003-260829 (for example, paragraphs [0053]-[0059], FIG. 5, FIG. 6, etc.), Japanese Laid-open Patent Publication No. 2010-194748 (for example, paragraphs [0046]-[0050], FIG. 5, etc.) (Patent Document 3), and Japanese Laid-open Patent Publication No. 2007-276135 (for example, paragraphs [0072]-[0081], FIG. 5, FIG. 8, etc.) (Patent Document 4) are examples of the related art.